Cement compositions with which the invention is concerned includes concretes which comprise cement aggregate, sand and water; mortars which comprise cement, sand and water; lime sand and water or mixtures containing both lime and cement. High pressure steam cured concretes comprising cement aggregate and water, lime or limestone and siliceous materials such as silica flour and water are also included. The improved physical characteristics produced in cement compositions prepared according to this invention result from air entrainment. The entraining of air in such compositions is known to improve durability of concretes, particularly resistance to frost damage and also improve the flow characteristics, which are of importance for cement pumping and other concrete placing operations. The working characteristics of mortars are also improved by entraining a proportion of air which can reduce the proportion of lime required in the composition.
It has been proposed to utilize pulverised fuel ash, also referred to as flyash, as a component in concretes and the requirements for such a component are given in British Standard 3892 (Part 1) 1982, however the present invention is not limited to the fuel ashes described in this standard. The pulverised fuel ash, as it will be termed in this specification, is the ash residue from pulverised fuel. The Applicants have found the presence of carbon in the fuel ash reduces the ability of air entraining agents to operate effectively.
Thus the present invention describes cement compositions having a proportion of pulverised fuel ash as a component, usually up to about 65% and having a loss on ignition up to about 12%, with an air entrainment agent which is effective despite the presence of the carbon.